1. Field of the Invention
The present invention relates to an oil temperature adjusting apparatus which is applied mainly to a hydraulically operated transmission for a vehicle.
2. Description of the Related Art
The hydraulically operated transmission for the vehicle is composed of a fluid torque converter adapted to be connected to an engine and a sub transmission including hydraulic clutches for gear shifts and mounted on an output side of the fluid torque converter. The fluid torque converter is provided with a lock-up clutch which is adapted to be pushed toward a side of engagement by hydraulic pressure in its inner gap and pushed toward a side of release by hydraulic pressure in a back pressure chamber. The lock-up clutch is so constructed as to be engaged either in a direct coupling condition or in a slipping condition, by controlling a differential pressure between the hydraulic pressure in the inner gap and the hydraulic pressure in the back pressure chamber.
In this structure, when the lock-up clutch is engaged in the slipping condition, oil temperature of hydraulic fluid will rise with friction heat. Conventionally, the temperature of the hydraulic fluid in the transmission has been prevented from rising, by returning the oil drained from the fluid torque converter into a transmission case through a radiating pipe arranged on a rear face of a radiator.
By the way, as the oil temperature of the hydraulic fluid in the transmission becomes low, a friction loss of the transmission will become large due to an increase of viscosity of the hydraulic fluid, and fuel efficiency in the engine will be deteriorated. However, a conventional attention has been paid only to prevention of the temperature rise of the hydraulic fluid, and accordingly, when the temperature of the outside air has become low, the temperature rise of the hydraulic fluid has been deferred, which has caused a bad influence on the fuel efficiency.
In view of the above, it is an object of the invention to provide an oil temperature adjusting apparatus in a hydraulically operated transmission in which the temperature rise of the hydraulic fluid in cold weather can be accelerated and the fuel efficiency can be improved.
In order to solve the above described problem, there is provided according to the invention, an apparatus for adjusting oil temperature of hydraulic fluid in a hydraulically operated transmission which is adapted to be connected to an engine, wherein the apparatus includes a heat exchanger for conducting heat exchange between the hydraulic fluid and cooling water for the engine.
Temperature of the cooling water for the engine will rise in an early stage after the engine has started, and the temperature rise of the hydraulic fluid will be accelerated by conducting the heat exchange with the cooling water. Thus, even in the cold weather, the temperature of the hydraulic fluid will be raised in an early stage and the friction loss in the transmission will be reduced, so that the fuel efficiency can be enhanced.
Moreover, when the oil temperature of the hydraulic fluid has become over a determined level, the cooling water for the engine acts as a cooling medium to cool the hydraulic fluid, thus preventing the hydraulic fluid from being overheated.